During female meiosis, 3/4 of the chromosomes are eliminated and only 1/4 of the chromosomes are inherited by a single egg. In contrast, all chromosomes are distributed among 4 sperm during male meiosis. The elimination of 3/4 of the genome to allow inheritance of only 1/4 of the chromosomes is conserved in all animal phyla, suggesting some fundamental selective advantage. The long-term goals of this project are to elucidate the molecular mechanisms of chromosome elimination and elucidate the selective advantages of asymmetric meiotic division. Errors in meiosis lead to the absence of one chromosome (monosomy) or the presence of an extra chromosome (trisomy) in 10-30% of human conceptions with the majority of these aneuploidies leading to embryonic death. By elucidating the mechanisms of meiotic chromosome elimination in C. elegans, we will identify mechanisms likely to be defective during human meiosis. In this project we will pursue 4 specific aims: 1. Elucidate mechanisms that prevent the sperm aster from capturing the oocyte meiotic spindle. 2. Determine how cytoplasmic dynein orients one spindle pole at the cortex. 3. Determine how katanin mediates acentriolar spindle pole assembly. 4. Test whether unpaired chromosomes are selectively extruded into polar bodies to prevent trisomy. These aims will be addressed by time-lapse imaging of fluorescent protein fusions within meiotic embryos that have been depleted of key cytoskeletal regulators and cell-cycle regulators by RNA interference and by protein biochemistry.